(57) 57 An electrochemical device for measuring oxygen partial pressure of a measurement
gas has a sensing cell which comprises a first planar solid electrolyte body 4, a
first and a second porous ele6trode 20, 22 on the first electrolyte body, the second
electrode being exposed to a reference gas, and a member 2 which has a predetermined
diffusion resistance to a measurement gas and covers the first electrode. An electric
current is applied between the first and second electrodes, to induce an electrode
reaction to control the atmosphere adjacent to the first electrode. To make the device
capable of measuring not only oxygen partial pressure of lean-burned exhaust gas but
also the amount of unburned components in a rich-burned exhaust gas, the device has
a pumping cell which comprises a second planar solid electrolyte body 8, and a third
and a fourth electrode 24, 26 of porous structure on the second electrolyte body.
The third electrode is exposed to the said reference gas and the fourth electrode
is exposed to the measurement gas. An electric current is applied to flow from the
third electrode to the fourth electrode, whereby an oxygen component of the measurement
gas is moved into the reference gas.
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